Biomechanics of mandibular torus development in response to lateral loading

Objectives: Mandibular torus appears on the lingual surface of the mandibular premolar region. Functional stress is considered to be one of the etiologic factors of torus development. However, few studies have examined this etiology from a biomechanical point of view. This study was undertaken to evaluate the biomechanical response of dentulous mandibular bone when load was applied on the premolar. Methods: A linear 3D finite element model of the dentulous mandible was reconstructed, containing dentition, PDL, and mandibular bone. The tooth was segmented into enamel, dentine, and dental pulp. Shapes of these constituents and the elastic modulus of mandibular bone were determined from CT images. A load of 100 N was applied on the buccal cusp of the left second premolar in three directions: lateral loadings with 45° inclination to the lingual and buccal sides, and axial loading along the tooth axis. Commercially available computer software, Mechanical Finder (RCCM, Tokyo) was used for modeling and FE simulation. Maximum and minimum principal stresses were examined on both buccal and lingual surfaces of the mandible at the apical areas of the loaded tooth. Results: Buccally and lingually inclined loading resulted in higher tensile and compressive stresses, respectively, at the apical areas on both lingual and buccal surfaces, whereas these stresses were not found under axial loading. In addition, the stresses on the lingual and buccal surfaces were parallel and perpendicular to the occlusal plane, respectively, regardless of the direction of lateral loading. Conclusion: These findings could explain torus development from a biomechanical point of view and lingual site presentation of the torus; the lateral force acting on the tooth may play a significant role in mandibular torus development.